This was David's advice to me for our upcoming expedition to Alaska's Harding Icefield, emailed along with a link to Glacier Mountaineering: An Illustrated Guide to Glacier Travel and Crevasse Rescue.

I am no stranger to mountains, having grown up in Colorado and spent several seasons building trail, backpacking, doing biological research and writing in the state's stretch of the Rockies. But glaciers were a mystery to me -- and the Harding is the largest icefield in the United States. Together with the more than 30 glaciers that flow from it, it covers 700 square miles of the Kenai Peninsula and may be a mile thick in places. A Google search yielded pictures that were both alluring and bowel-watering, but no travel accounts. What, I wondered, had I gotten myself into when I agreed to accompany author Craig Childs, David Stevenson, John McInerney and adventure photographer James Q Martin on a research trip for Craig's book exploring ancient human migration?

I wrote back to David, an experienced mountaineer: Should I do anything else to prepare? Probably not, he replied. Then, "Full disclosure: McInerney says that my default answer is, 'It will be fine.' When he hears me say that, he interprets it as, 'Stevenson is a lunatic, who has a death wish.' "

Great, I thought, and bought the book.

So it is that in the last days of May, after last-minute shopping in Anchorage, a winding drive south to Seward, and an encounter with a woman who gives us a ukulele like a blessing at the Kenai Fjords National Park visitor's center, I find myself post-holing two heavy loads 3,500 vertical feet up a snow-covered ridge to our first camp. It feels good, the weight -- a confirmation of my strength on a journey that is otherwise so new to me that I can't help feeling uneasy. When I finally release my pack from my shoulders, the icefield sprawls before me. Its vast whiteness gathers and scatters light, compresses and stretches distance, pillowing around the peaks of submerged mountains called nunataks and pouring in a blue-and-black-streaked cascade to the Resurrection River Valley as the Exit Glacier. My breath stops, stutters back.

The book informs me that this sort of whiteness can literally devour you. You may have to negotiate crevasses, which can form anywhere ice passes over an obstacle or changes elevation, and are sometimes disguised by snow. You may have to cross cracks called bergschrunds where ice pulls away from mountainsides, which tend to be hundreds of feet deeper than crevasses.

But the Harding will swallow us in a different way. The snow ramping onto it appears smooth and consolidated, so David and Q decide we don't need ropes. As we kick steps, passing an unearthly blue lake and eerie melt holes left by fallen rocks, I pester David about cracks and depressions in the snow, trying to learn to read it the way he has. After an uneventful hour, I realize that I have been running over the names of people and places I love in my head, whispering thankyou and thankyou and thankyou. I laugh at myself, wondering how long it's been since my mind was clear of all save the things I'm grateful for.